7196

• UCREFRP Catalog Number: 7196
• Author: O'Brien, J. S.
• Title: Hydraulic and Sediment Transport Investigation Yampa River Dinosaur National Monument 1983 Final Report.
• USFW Year: 1984.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

56
Combining the historical mean daily discharge with the simulated
daily discharge, whichever is less, a composite hydrograph is developed
(Figures 24-30). The results are presented in Table IX. The minimum
streamflow hydrograph has the following components:
Baseflow (August 16 - March 21)
Of the three periods of record analyzed, water years 1922-83,
1922-38 and 1941-83, the mean baseflow (367 cfs) of the 1941-83 period
was chosen as reflecting the post-expansion conditions in the Monument.
Rising and Recessional Limbs (March 22 - July 12)
This portion of the hydrograph was defined by the criteria for
maintaining the river mile 16.5 cobble bar essentially free of sand in
July and early August.
Colorado Squawfish Spawning Flows (July 12 - August 15)
The PHABSIM computer model predicted 700 cfs to be the optimal flow
for spawning.
Peak Flow (May 24 - June 20)
The peak flow of 11,500 cfs is the computed effective discharge at
Mathers Hole based on sediment rating curves. A channel flushing flow
of 48 hours of natural peak is included in the composite hydrograph.
When the simulated discharge equals or exceeds the 11,500 cfs peak, then
the actual peak discharge and next daily discharge less than or equal to
21,000 cfs is included in the simulated hydrograph. This constraint is
reflected in Table IX in computing the composite volumes but was not
used in the computer model.
The various components of
increments. One week steps were
of water and sediment discharge
was associated with each step.
rapid changes in discharge. Only
analyzed by the model; local
fluctuations are neglected.
the hydrograph are connected by step
utilized in the model. A single value
representing the average for the week
This methodology does not allow for
general aggradation and degradation is
scour, storm inflow, and hydrograph
Cross section subreach 5 (Figure 3) was determined by the model. to
be sensitive to aggradation and degradation of transported sand. It is
also the reach where substantial amounts of aggradation could influence
distribution of water discharge around the cobble island. The next
subreach upstream of cross section 5 is predominantly sand bed and the
downstream reach, mostly cobbles.
Water discharge input was varied to show how sensitive each
subreach was to sand deposition. Incremental discharges were input
until most of sand deposited is removed and does not exceed one-half of
the median cobble diameter in thickness after July 11th. Figure 31 shows
the bed elevation response to the simulated discharge hydrograph at
subreach 5. Sand is deposited during the rising limb of the hydrograph
and removed during the recessional limb.